Ad interesting little book has been issued by the London County Council descriptive ot the Biuckwall Tunnel recently opened bv the Prince of Wales, the opening of tl*e tunnel inaugurating the only free crossing of the Thames between the" Tower Bridge pnL Woolwic!l Fert 7- The tunnel cost £900,000 in round figures, Messrs Mowlen and Co., the constiuctors, commencing work in 1592 and finishing in 1897. The total length from entrance to entrance is about one mile and a quarter, the roadinc is 16ft wide, having 17ft Gin headway to the centre, and there is a footpath on each side. The portion under the river is level. An electric installation has been put no, the test being to read a newspaper in any part of the tunnel. To ensure the safety of the workmen and to prevent the compressed air blowing up the ground above the large shield used in the course of construction, a layer of clay 10ft thick and 150 ft wide was deposited on the river bed from barges over the line of the tunnel, but even this did not suffice, as on two occasions holes were blown in the bed of the river and the water poured into the tunnel, but each time the men escaped without accident. About half the tunnel has been constructed of cast iron, instead of the usual brickwork the advantage claimed for the iron being that as soon as erected the lining has attained its full strength, which in the case of brickwork requires years. The external diameter of the cast-iron lining is 27ft, which constitutes a record in the size of tunnels constructed in this way. A steel shield was used as being necessary for the rapid construction of the work and the safety of the men employed. It was driven forward by means of hydraulic rams. The enormous water pressure of 2J tons to the square inch was used, and the total pressure thrusting the shield forward was at times 5,000 tons The total time occupied in the construction of the work was a little over five years, but a year of this time was occupied in preparatory work, such as diversion of sewers and work of a similar nature. The portion of the tunnel underneath the Thames was constructed in almost exactly twelve month?, which is at the average rate of 100 ft per month. Access to the tunnel for vehicular traffic is necessarily at each end only, but provision is made for foot passen. gers at four additional points. The book contains a number of illustrations of the work during its different stages and at com. pletion, the last being not only most interestin? but exemplying most clearly the magnitude of the work. The surface of the river teems with shipping of all sorts and conditions, while several feet below the bed is this triumph of man's enterprise, the tunnel, white with the blaze of the eleotrio light, vehioles of all descriptions passing one another, and the footways crowded with passengers, while on the external sides of the tunnel are the green sand, chalk and shell deposits of generations through which the tunnel has been cut.
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BLACKBALL TUNNEL., Evening Star, Issue 10451, 22 October 1897
BLACKBALL TUNNEL. Evening Star, Issue 10451, 22 October 1897
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